Abstract The specification discloses a digital cryptographic system operating under a digital coding scheme having forbidden control characters with common bit characteristics. In the encoding mode, clear digital data and randomized digital data are stored and selected bits of the clear and randomized digital data are modulo-2 added. The added bits are then examined to determine whether or not the bits have the common bit characteristics of the forbidden control characters. If so, the selected bits of the stored clear digital data are varied to prevent the subsequent generation of forbidden control characters in the encoded data. The clear digital data and randomized digital data are then modulo-2 added to generate encoded data. The present system is compatible with eight-level digital codes and the system includes parity bit checking techniques to ensure accuracy of operation. The present system may be operated as either an On-line or Offline system and may be utilized to provide security of digital transmission between teleprinters or between a teleprinter and a digital computer or the like.
Inventors
👤 Barrie O Morgan
👤 Kenneth M Branscome
👤 George E Goode
👤 John Q Atchley
Bibliographic Details
Application Number—
JurisdictionUS
Data Sourcegoogle_patents
Last Synchronized2026-10-28 18:26
CPC Classifications
H; H04; H04L; H04L9/00; H04L9/36
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
141 words
In a cryptographic system, a parity check system comprising: means for transmitting enciphered digital data having a parity bit, means for receiving said enciphered digital data from said transmitting means and for detecting said parity bit, means for checking the parity of preselected bits of said enciphered digital data and for storing an indication of whether or not the checked parity matches said parity bit, means connected to said receiving means for deciphering said enciphered digital data to generate clear digital data, and means responsive to said detecting and checking means for regenerating a parity bit for said clear digital data such that the parity of said clear digital data corresponds with the detected parity of said enciphered digital data, in order to prevent the generation of incorrect parity indications for the clear digital data due to deciphering of said data.
Claim 2
Dependent Claim
141 words
In a cryptographic system, a parity check system comprising: means for transmitting enciphered digital data having a parity bit, means for receiving said enciphered digital data from said transmitting means and for detecting said parity bit, means for checking the parity of preselected bits of said enciphered digital data and for storing an indication of whether or not the checked parity matches said parity bit, means connected to said receiving means for deciphering said enciphered digital data to generate clear digital data, and means responsive to said detecting and checking means for regenerating a parity bit for said clear digital data such that the parity of said clear digital data corresponds with the detected parity of said enciphered digital data, in order to prevent the generation of incorrect parity indications for the clear digital data due to deciphering of said data.
Claim 3
Dependent Claim
29 words
The cryptographic system of claim 1 wherein said system operates with an eight level coding scheme wherein each eight bit word includes a parity bit to enable error detection.
Claim 4
Independent Claim
84 words
A method of parity checking in a cryptographic system comprising: detecting the parity bit of a received encoded digital word, checking predetermined bits of said digital word to determine whether or not the checked parity matches said parity bit, storing said checked parity, decoding said encoded word to generate a clear digital word, and regenerating and adding a parity bit to said clear digital word such that the parity of said clear digital word corresponds to the detected parity of said encoded digital word.
Claim 5
Independent Claim
84 words
A method of parity checking in a cryptographic system comprising: detecting the parity bit of a received encoded digital word, checking predetermined bits of said digital word to determine whether or not the checked parity matches said parity bit, storing said checked parity, decoding said encoded word to generate a clear digital word, and regenerating and adding a parity bit to said clear digital word such that the parity of said clear digital word corresponds to the detected parity of said encoded digital word.